Chemical Stability and Leaching Behavior of One-Part Geopolymer from Soil and Coal Fly Ash Mixtures
Chemical Stability and Leaching Behavior of One-Part Geopolymer from Soil and Coal Fly Ash Mixtures
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DOI：
10.3390/min8090411
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发表时间：
2018-09-01
期刊：
影响因子：
2.5
通讯作者：
Promentilla, Michael Angelo B.
中科院分区：
文献类型：
--
作者：
Tigue, April Anne S.;Malenab, Roy Alvin J.;Promentilla, Michael Angelo B.
铝硅酸盐矿物已成为一种新兴的可持续建筑材料（称为地质聚合物）的重要资源。地质聚合物是一种碱活化材料，由于其较低的碳足迹和隐含能量，正成为波特兰水泥的有吸引力的替代品。然而，合成方法通常需要用于碱活化的两部分系统，其中固体地质聚合物前体与碱水溶液混合。这些碱性活化剂具有腐蚀性，并且在现场规模应用中可能难以处理。在这项研究中，一个单组分的地质聚合物，粉煤灰与固体碱激发剂，如氢氧化钠和硅酸钠混合，形成一个粉末状的水泥基粘结剂的开发。这种与土壤混合的粘合剂只需要水就可以形成土壤-粉煤灰（SO-CFA）地质聚合物水泥，它可以用作回填/地基的稳定土。然后通过将该材料用5重量%的硫酸溶液浸泡28天来评估该地质聚合物产品的化学稳定性。指示表明，地质聚合物表现出高的抗酸侵蚀性，观察到的无侧限抗压强度的增加，即使当在酸性溶液中的浸泡时间增加到56天。采用X射线衍射（XRD）、傅里叶变换红外（FTIR）光谱和扫描电子显微镜-能量色散X射线能谱（SEM-EDX）对材料的物相、显微结构和形貌进行了表征。结果不仅证实了由于酸侵蚀而形成的石膏，而且还表明钙长石和钠长石的溶解可能导致微观结构由具有聚（铁-sialate-dibrio）和聚（铁-sialate-dibrio）网络的水合铝硅酸钠（N-A-S-H）和水合（铝）硅酸钙（C（-A）-S-H）组成。用去离子水对土壤-粉煤灰地质聚合物进行柱浸出试验，以研究材料中金属的可溶解性。结果表明，砷表现出较高的流动性，在地质聚合物相比，镉，铬，铅。
Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N-A-S-H) and calcium (alumino) silicate hydrate (C(-A)-S-H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.